Goldschmidt 2012 Conference Abstracts
Petrogenesis of Cenozoic plateau
lavas from the Pali Aile Volcanic
Filed and Morro Chico Volcano,
southern Patagonia in South
America
MI KYUNG CHOO1,2* , MI JUNG LEE1, JONG IK LEE1, KYU HAN
KIM2 AND KYE-HUN PARK3
1
Korea Polar Research Institute (KOPRI), Incheon, Korea,
mkchoo@kopri.re.kr (* presenting author), mjlee@kopri.re.kr
and jilee@kopri.re.kr
2
Ewha Womans University, Seoul, Korea, kyuhan@ewha.ac.kr
3
Pukyong National University, Busan, Korea, khpark@pknu.ac.kr
Geochemical and Sr-Nd-Pb isotopic analyses of late Miocene to
Quaternary plateau lavas from the Pali Aike Volcanic Field (PAVF)
and Morro Chico Volcano (MCV) (52°S) were undertaken to
constrain the melting processes and mantle sources that contributed to
magma generation and the geodynamic evolution of southernmost
Patagonia, South America. The PAVF and MCV lavas are alkaline
(PAVF, 45–49 wt% SiO2; 4.3–5.9 wt% Na2O+K2O) and subalkaline
(MCV, 50.5–50.8 wt% SiO2; 4.0–4.4 wt% Na2O+K2O), relatively
primitive mafic volcanic rocks that have typical intraplate ocean
island basalt-like signatures. Incompatible trace element ratios and
isotopic ratios of the PAVF and MCV lavas differ from those of the
majority of Neogene southern Patagonian slab window lavas in
showing more enriched characteristics and are similar to high-μ
(HIMU) end-member basalt. The REE melting model suggests that
these lavas were produced by low degrees of partial melting of a
garnet lherzolite mantle source. The major systematic variations of
Sr-Nd-Pb isotopes in southern Patagonian lavas are related to
geographic location. The PAVF and MCV lavas from the
southernmost part of Patagonia have lower 87Sr/86Sr and higher
143
Nd/144Nd and 206Pb/204Pb ratios, relative to most of the southern
Patagonian lavas erupted north of 49.5°S, pointing to a HIMU-like
signature. An isotopically depleted and HIMU-like asthenospheric
domain may have been the main source of magmas in the
southernmost part of Patagonia, suggesting the presence of a major
discontinuity in the isotopic composition of the asthenosphere in
southern Patagonia. On the basis of geochemical and isotope data and
the available geological and geotectonic reconstructions, a link
between the HIMU asthenospheric mantle domain beneath
southernmost Patagonia and the HIMU mega-province of the
southwestern Pacific Ocean is proposed.
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